Being able to accurately determine the efficiency of detection, in respect of having precise measurements of radioactivity, represents one of the main objectives of every gamma spectrometry laboratory. In standard gamma spectrometry practice, activities of low-energy emitters can prove to be difficult for measurement. Gamma spectrometry is often used as an initial monitoring tool to determine basic parameters of the unknown sample found in the field, especially when it is suspected that this material can be a part of illicit trafficking involving radioactive materials. The main concern in most cases is uranium, as one of its isotopes (²³⁵U) can be used in the production of a nuclear bomb. Gamma spectrometry is the most applicable, non-destructive technique used in a nuclear forensic investigation for uranium isotopic composition analysis.

The main idea of this paper was to test the advantages and disadvantages of semi-empirical methods by using two software (EFFTRAN and Angle) and simulation method in GEANT 4 applied on samples containing uranium and thorium isotopes. Special attention was devoted to non-cylindrical sample geometries. The general purpose of the presented study was to investigate the possibilities of routine gamma spectrometry laboratory to be able to respond to a nuclear security event.

Based on the obtained results, general recommendations for the use of semi-empirical and simulation methods are given.

就放射活性的精确测量而言，能够准确确定检测效率是每个伽马能谱实验室的主要目标之一。在标准的伽马能谱实践中，低能量发射器的活动可能难以测量。伽马能谱通常用作确定现场未知样品基本参数的初始监视工具，尤其是在怀疑这种物质可能是涉及放射性物质的非法贩运活动的一部分时。在大多数情况下，主要关注的是铀，因为它是同位素之一（²³⁵U）可用于生产核弹。伽马能谱法是用于铀同位素组成分析的核法证研究中最适用的非破坏性技术。

本文的主要思想是通过使用两个软件（EFFTRAN和Angle）以及GEANT 4中的模拟方法对含铀和or同位素的样品进行测试，以检验半经验方法的优缺点。特别注意非圆柱样品的几何形状。本研究的总体目的是研究常规伽马能谱实验室对核安全事件做出反应的可能性。

根据获得的结果，给出了使用半经验和模拟方法的一般建议。